This invention relates to acoustic stringed musical instruments and, more particularly, to devices and arrangements for enhancing the low frequency response of such instruments.
Recently, one stringed instrument, the acoustic guitar, has been provided with bodies that are relatively thinner than prior traditional instruments. Although the thins body instruments are easier and more comfortable to play, because of the thinner bodies, an unfortunate trade off results. A detrimental side effect based upon the acoustics and physics is created when making an acoustic string instrument with a thinner than traditional body. One problem is less air space in the instrument""s body resonating cavity (this volume or space) used to effectively generate a micro air current when a string is struck, results in sympathetic vibration, i.e., available air mass and consequently effective volume and low frequency response is reduced. The result is less air mass available for the strings (especially for the low frequency strings, typical examples: E or D strings) to create vibrations which resonate in the body cavity. Another result is that in such thin body instruments, volume (loudness measured in Db or DBSPLxe2x80x94decibels measured by sound pressure level) and the subsequent resulting low frequency response characteristics are effectively reduced.
Over the years, manufacturers have attempted to compensate for the reduced low frequency response and volume (loudness) with electronic sound conditioning devices, such as: electronic equalizers, volume controls and boost circuitry built into the body, which are tied into an internal microphone, electronic pick up, or other electronic sound detection or amplifier devices.
The draw back of all of the above mentioned electronic sound conditioning compensation devices is that they are working in a low frequency and volume impaired body cavity environment, which does not produce vibrations in a range comparable to the rich full frequency sound spectrum of a full size or traditional model as a source. Thus, the prior art electronic pick up and amplifying devices as recognized by the present inventor amplify acoustic waves that are initially deficient in their overall response characteristics in the low frequency spectrum, i.e., at approximately and below about 500 Hz.
Sympathetic strings have been used in the prior art in an attempt to increase resonance. These strings are located in the instrument body resonating chamber and are intended to respond to incidental acoustic energy in the chamber. These strings are intended to vibrate sympathetically in response to incident acoustic energy, i.e., sympathetic vibrations are vibrations which resonate at the fundamental or harmonic frequencies of the incident acoustic energy. The problem with such strings, as recognized by the present inventor, is that the sympathetic string system lacks the mass or area to move sufficient amounts of air to effectively increase volume and low frequency response characteristics to be acoustically effective to a listener.
A string instrument according to an embodiment of the present invention comprises a body having a resonant chamber; at least one string manifesting a tone of a given frequency secured externally of and to the body and of the chamber for producing first acoustical waves in a range of frequencies, the chamber exhibiting second acoustic (e.g., sympathetic) waves in a range of frequencies responsive to and corresponding to the first waves; and acoustic wave enhancing means coupled to the body and to the chamber for enhancing the lower frequency portion of the range of frequencies of the second waves.
The acoustic wave enhancing means preferably comprises a passive radiator secured to the body, and responsive to the second waves for producing sympathetic acoustic waves that contribute to increased low frequency response and volume.
The body has front and rear faces, the strings are strung over the front face, the passive radiator may be either in the body rear face, the front face or both. The passive radiators in the corresponding front and rear faces may be identical or different dimensions and/or configurations and may be flush with or recessed in the rear face. The passive radiator configuration, shape, material, front or rear position and size will depend on the instrument being modified.
The acoustic wave enhancing means may also comprise isolated resonating tuned wave guide means secured to the body in the chamber and may comprise a planar sheet member secured to spaced posts, the posts being secured to the body and may be secured to the rear or front faces.
In a further aspect, the wave guide means may comprise a plurality of spaced planar sheet members each secured to a pair of spaced posts, the posts being secured to the body, the spacing size, width, height, thickness, flexibility and subsequent acoustic sensitivity of the sheet members are arranged for tuning the isolated tuned resonating wave guide means. The wave guides may be arranged in cooperating pair sets each set having a given tuned frequency response or as a single wave guide.
The front face may optionally have an opening, sometimes referred to as the sound hole, in communication with the chamber, the wave guide(s) direct waves in the low frequency portion of a range of frequencies in the chamber toward the opening.
The strings each generate an acoustic wave of a given frequency and its harmonics in a range, and in a further aspect, the opening in the front face may have a portion adjacent to the lower frequency strings that is sufficiently large to correspond to and enhance the passage therethrough of lower frequencies of the second waves to enhance the volume of the generated waves. The opening portion may be transversely larger in the direction of the strings that generate lower frequencies than the remainder of that opening. The opening may be generally triangular, T or L-shaped. The shape of the openings may emulate the curve(s) and slope(s) of a graphic or parametric equalizer in a non-electronic (acoustic) form. The result is an emphasis on the reproduction of desired frequencies. This is accomplished by allowing more low frequency waves into the resonating body and reflecting the string generated higher frequency waves from the front face
The acoustic wave enhancing means in a further aspect comprises means for enhancing the harmonics of the frequencies of the lower frequency strings. The acoustic wave enhancing means in a further aspect comprises means for enhancing fundamental tones of the lower frequency strings.
The acoustic wave enhancing means preferably comprises means for increasing the number of generated lower frequencies, and the volume measured in Db and DBSPL of the tones produced by the lower frequency portion of the strings.
The acoustic wave enhancing means may comprise acoustic responsive means exhibiting a response that is a manifestation of an increased volume (loudness) comprising enhanced low frequency sympathetic vibration. Such increased volume and/or enhanced vibration produce an acoustic response that sounds more natural to the human ear for a given instrument. This increased volume and enhanced vibration is a simulation of a full size (e.g., deeper body cavity) instrument. When electronically picked up (detected with a microphone) and reproduced via amplification, the enhanced resulting sounds appear similar to an original full body instrument. Such enhancement may also be provided a full body instrument to further enhance its low frequency response.
The size and location of the passive radiator depends on the application and degree of effect (frequency response and volume) desired. The passive radiator functions with or without a sound hole in the front face. The passive radiator may be used in conjunction with isolated tuned resonating wave guides which serve to enhance and direct sound waves and increase sympathetic vibration in consort with the passive radiator. Hence, both the passive radiator and the wave guides when used in conjunction directly increase low frequency reproduction, volume and directionality in the body cavity of a string instrument. These devices similarly effect (at present, to a lesser degree) solid body string instruments.
In a further embodiment, the body has a directive curved side wall(s) connecting the front and rear faces. The acoustic wave enhancing means includes a planar side wall portion of the side wall for providing directionality to the sound waves in the body chamber.
All of the enhancement means may be combined to provide a cumulative enhancement effect.